Fatigue Analysis of Flexible Joint Elastomers Combining Ogden Second-Order Constitutive Model with Cracking Energy Density

Abstract

As the core component of the flexible nozzle on solid rocket motors, the flexible joint relies on the shear deformation of its silicone rubber elastomers to achieve a large vector angle, and the joint is prone to fatigue failure when working under high pressure. Aiming to resolve the fatigue failure of flexible joint elastomers, the cracking energy density (CED) method was introduced into the fatigue analysis of flexible joints. A convenient integral formula for calculating the CED of elastomers was derived from the Ogden second-order constitutive model. The CED at the maximum value of the first principal elongation of the joint under 12.3 MPa and 6° swing angle was calculated by the finite element analysis (FEA), and then the fatigue life prediction of elastomers was conducted. The results show that the CED method can better predict the swing fatigue life and cracking plane orientation of elastomers compared with the SED. The results also show that the derived formula can efficiently and accurately obtain the CED distribution of the dangerous area of elastomers under load. The ratio of predicted life to measured life is 1/1.12 within the double dispersion factor. The predicted crack location and cracking plane orientation agree well with the fatigue test result. The method can provide a theoretical reference for fatigue analysis and structural reliability design of flexible joints.

Keywords

• flexible joint
• cracking energy density
• fatigue life prediction
• finite element analysis
• solid rocket motor